1. Field of the Invention
The present invention relates to a common-voltage compensation circuit and compensation method, and more particularly, to a common-voltage compensation circuit and compensation method for use in a liquid crystal display so as to suppress crosstalk interference.
2. Description of the Prior Art
Along with the advantages of thin appearance, low power consumption, and low radiation, liquid crystal displays have been widely applied in various electronic products for panel displaying. The operation of a liquid crystal display is featured by varying voltage drops between opposite sides of a liquid crystal layer for twisting the angles of the liquid crystal molecules in the liquid crystal layer so that the transmittance of the liquid crystal layer can be controlled for illustrating images with the aid of the light source provided by a backlight module.
It is well known that the polarity of voltage drop across opposite sides of the liquid crystal layer should be inverted periodically for protecting the liquid crystal layer from causing permanent deterioration due to polarization, and also for reducing image sticking effect on the liquid crystal display. Accordingly, various inversion operations, such as frame-inversion driving operations, line-inversion driving operations, pixel-inversion driving operations and dot-inversion driving operations, are developed to drive the liquid crystal display for improving image display performance.
FIG. 1 is a circuit diagram schematically showing a prior-art liquid crystal display 100. The liquid crystal display 100 comprises a plurality of data lines 110, a plurality of gate lines 120, a plurality of pixel units 130 and a common voltage generator 190. As shown in FIG. 1, for ease of explanation, the liquid crystal display 100 illustrates only a data line DLi, a gate line GLj and a pixel unit Pij. The pixel unit Pij includes a data switch 135, a liquid-crystal capacitor Clc and a storage capacitor Cst. The data line DLi is employed to deliver a data signal SDi and the gate line GLj is employed to deliver a gate signal SGj. The data switch 135 makes use of the data signal SGj for controlling a writing operation of the data signal SDi so as to generate a desired pixel voltage Vij. The common voltage generator 190 is utilized for providing a common voltage Vcom furnished to a common electrode COM via a conductive line. It is well known that parasitic capacitor Cd exists between the data line DLi and the common electrode COM and, further, parasitic capacitor Cg exists between the gate line GLj and the common electrode COM. For that reason, both the voltage changes of the data signal SDi and the gate signal SGj have an effect on the common voltage Vcom at the common electrode COM. In order to suppress the voltage variation of the common voltage Vcom caused by the data signal SDi and the gate signal SGj via the parasitic capacitors Cd and Cg, an external capacitor Cext is commonly installed for stabilizing the common voltage Vcom.
FIG. 2 is a schematic diagram illustrating a display image 200 of the liquid crystal display 100 shown in FIG. 1. Regarding the exemplified display shown in FIG. 2, the display image 200 can be sectioned into a first image area 210, a second image area 220, a third image area 230 and a fourth image area 240. The first image area 210, the second image area 220 and the fourth image area 240 have an image output with a first brightness in response to a first data signal. On the other hand, the third image area 230 has an image output with a second brightness in response to a second data signal different from the first data signal. Accordingly, the second brightness is different from the first brightness. In view of that, the first image area 210, the second image area 220 and the fourth image area 240 are supposed to have the same display brightness. Since the liquid crystal display 100 illustrates images based on the aforementioned inversion driving operations, the voltage polarity switching of the second data signal is able to affect the common voltage Vcom received by the pixel units 130 of the second image area 220 via the parasitic capacitor Cd while displaying the second image area 220 and the third image area 230. Consequently, the display brightness of the second image area 220 is actually different from that of the first image area 210 and the fourth image area 240, which is known as the crosstalk interference phenomenon of the liquid crystal display 100. That is, the display quality of the liquid crystal display 100 may be degraded due to an occurrence of image brightness distortion caused by crosstalk interference regarding the inversion driving operations.